Polarizing retinoscope



E, D. TILLYER POLARIZING BETINOSGOPE F116;! Nov. 22. 1937 2 Sheets-Sheetl B ww m N. m flm Patented Sept. 17, 1940 UNITED srA'rss PATENT oFFicPOLARIZING RETINOSCOPE Edgar D. Tillyer, Southbridge, Mass, assignor toAmerican Optical Company, Southbridge, Mass, a voluntary association ofMassachusetts Application November 22, 1937, Serial No. 175,865

g 4 Claims. (01. 8820) This invention relates to an eye examining fromthis source; and I have illustrated at C a instrument, and moreparticularly to an instrucondensing lens for directing approximatelyment which will project a beam of light into parallel (or slightlydivergent) rays of light upon the interior of the eye for diagnosticpurposes. the partially transmissive means R (or R1, R2,

5 The examination of the eyes was formerly and R3 in Fig. III).Accordingly, a beam of 5 handicapped by annoying reflexes from theanlight is directed into the eye P of the patient. terior surfaces ofthe cornea. The best method The line of sight A from the eye D of theEX- yet known for avoiding this difficulty is by poaminer, passesthrough the partially transmislarization of the light which is directedinto sive means E into the eye P (the light, of course, 1 the eye, usingan analyzer to eliminate the passes in the opposite direction from thatgiven). 10 light which is reflected from the anterior sur-. In theembodiment illustrated in Fig. I, a device face of the cornea. Ofcourse, any diffuse light N is used, which has such polarizing effectupon is not blocked out by the analyzer, so that the this returninglight as to function as an anretina and other surfaces which do notdirectly alyzer, and eliminate the annoying reflexes from 15 reflect thepolarized light can be viewed without the anterior surface of thecornea.

hindrance from the annoying reflexes from the In accordance with myinvention, I project reflecting surface of the cornea. polarized lightinto the eye of the patient by An object of the invention is to providea directing light from a light source upon the diagnostic instrumentwhich projects a beam reflecting surface of partially transmissive meansof polarized light into the eye of the patient, having this reflectingsurface arranged with the without the use of Nicol prisms or similardeangle of incidence substantially equal to the vices. polarizing angle.

Instruments which have been used for this In the accompanying drawingswhich illuspurpose heretofore, have required that the light trate myinvention:

emanating from the light source be passed Fig. I is a diagrammatic Viewillustrating one 25 through a Nicol prism, or some similar device,embodiment of my invention according to which thereby addingsubstantially to the cost of the a beam of light from the light sourceis reflected instrument. Moreaver, the capacity of the inby a singlesheet of glass into the eye of the strument to project light into theeye of the patient and the observer makes his examination 39 patient islimited by the characteristics of the by looking through a device havingsuch polarpolarizing device, such as the Nicol prism. This izing effectupon the returning light as to funcprism may be of such restricted areaas to limit tion as an analyzer; the amount of light which can be passedthrough Fig. II is a similar view of a second embodithe same. 7 ment ofmy invention in which this polarizing 3 A further disadvantage of aNicol prism, or device is omitted and the sheet of glass itself similardevice, is that its inefliciency in transfunctions as the analyzer;mitting light cuts down the available illumina- Fig. III is a similarview of a third embodition for the surfaces which are to be observed.ment of my invention, in which a plurality of The best polarizingdevices available cut down glass sheets are employed for increasing the40 the effective illumination to substantially less polarizing effect onthe light emanating from 40 than half. This, together with the loss atthe the light source; transparent mirror, which customarily is in- Fig.IV is a view in elevation from the Exeluded as a part of the diagnosticinstrument, aminers side of a diagnostic instrument emreduces theavailable illumination for the surbodying my invention; and

faces to be examined until the matter of suf- Fig. V is a view invertical section on the line 5 ficient illumination is a real problem.V-V of Fig. IV.

The advantage afforded by the present in- I find a sheet of glass to besuitable for the vention in the way of increased illumination partiallytransmissive means R. The beam of for the benefit of the observer willbe pointed light indicated by the line L, which is thrown out inconnection with the description of the upon the sheet of glass R, ispreferably of the 50 embodiments of my invention illustrated in Figs.character usually provided by diagnostic instru- I, II, and III of thedrawings. In each of these ments of this character. This light fallingupon embodiments, there is a light source shown as the inclined surfacesof the sheet of glass R is the filament of an electric lamp E. It is, ofseparated by these reflecting surfaces into two course, advantageous toconcentrate the light portions. One portion passes on through. The 55portion which passes along the line L1) is almost completely polarized.The other portion is partially polarized; but as it is not used, We arenot concerned therewith. The beam of light Lp, which falls upon and intothe eye of the patient P, is the light which illuminates the surfaces tobe observed. With the surfaces of the sheet R clean, and with the angleof incidence of the beam L substantially equal to the polarizing angle,a maximum portion of this light is directed, as polarized light Lp,toward the surfaces of the eye to be examined. By polarizing the light Lin this manner with partially transmissive means, the portion of thelight which is made available for illumination is relatively high.

It will be understood that the above mentioned angle of incidence shouldbe substantially equal to the polarizing angle which will depend uponthe index of refraction of the sheet R; and that accordingly this anglewill vary slightly, depending upon the type of material used for thepartially transmissive means. As

shown, this angle is about 66 It will be apparent, then, that a portionof the light in the beam L has been directed by the surfaces of thesheet R in a polarized condition, along the line indicated as Lp in Fig.I; and that this polarized light is employed in this diagnosticinstrument for illuminating the surfaces to be observed. As this lightin -a diffused condition returns from the retina through the partiallytransmissive means R, it is again divided into a polarized portion whichis reflected and lost, and into a portion which goes. on through to theeye D of the observer. It is this latter portion which presents to theeye D the picture or image of the surfaces which are being examined. Butother than this diffuse light, is also directed along the axis A. Asabove mentioned, there are objectionable reflexes from the anteriorsurface of the cornea. This is all polarized light, since it is a directreflection of the polarized light of the beam Lp. Moreover, thispolarized light is polarized in a single plane. Accordingly an analyzer,if properly arranged and constructed, will eliminate this polarizedlight.

In the embodiment shown in Fig. I, I employ a device N which has suchpolarizing effect upon the returning light A, as to function as ananalyzer. This device N may be a Nicol prism, or it may be a sheet ofcellulose acetate film, containing minute crystals arranged in parallelformation, these crystals. being so oriented as topolarize the light inthe desired plane. This type of material is sold under the trade-markPolaroid.

' Before the instrument is put into use, this device N is oriented so asto block out the polarized light reflected along the axis A.

In the embodiment shown in Fig. I, therefore, we have high efficiency ofillumination of the surfaces of the eye P with polarized light; and inthe line of sight to the eye D of the examiner has been inserted ananalyzer N, which prevents any substantial amount of polarized lightfrom entering the eye of the observer.

The polarizing device N, of course, cuts down the amount of lighttransmitted to the eye D at least one-half. Such devices are soefficient in their polarizing effect that their use is desirable.provided there is enough light in the first place, so that even when outdown more than one-half, the observer is able to see clearly thesurfaces he is examining. At the expense of some annoyance from theabove mentioned reflexes, it is possible to do away with the device N;and Fig. II of the drawings illustrates my invention with such omissionof the device N. The omission of the device N leaves the function ofanayzer to the sheet R. The angle of incidence of the polarized lightpassing along the axis A upon the sheet R is substantially thepolarizing angle. Not all of this polarized light traveling toward theeye D is reflected by the sheet R, however. Accordingly, there isbalanced against the increased amount of light entering the eye D, theannoyance of a substantial amount of polarized light passing through thesheet R instead of being deflected.

In the embodiment illustrated in Fig. III, a plurality of sheets R1, R2and R3, of partially transmissive means are employed, instead of thesingle sheet R. As the rays of light are directed from the source E uponthese sheets R1, R2, and R3, each surface acts in the manner abovepointed out, namely, to separate the rays of light into a portion whichis polarized and reflected, and a portion (also polarized) Which passeson through. The added effect of the four surfaces of the added sheets R2and R3, means an augmented beam Lpfor illuminating purposes.

At the same time, the returning light along the axis A passes throughthree sheets. This means that each of these sheets functions as ananalyzer, and the cumulative effect of the three sheets is suflicient tocut down. the annoyance from reflection of polarized light to a pointwhere it can be disregarded. In the embodiment illustrated in Fig. III,therefore, the device N will ordinarily be omitted, although it may beemployed to remove the last traces of reflected polarized light.

Against the advantage of the embodiment shown in Fig. III that there isincreased eificiency both in the amount of polarized light directedtoward the eye P and in the analyzing effect upon the reflectedpolarized light, there is balanced the susceptibility of thisconstruction to infiltration of dirt between the sheets R1, R2, and R3.The eii'iciency of such an arrangement, therefore, depends upon thewillingness of the user to keep these surfaces clean. It will beunderstood that tiny particles of dust upon the surfaces of these sheetsR1, R2, and R3, have a bearing upon the efficiency of the instruments,as such tiny particles act upon polarized light to diffuse the same. Itis important, therefore, that the surfaces of the partially transmissivemeans be clean.

Of the three embodiments I have selected for illustration in detail thefirst two embodiments and Figs. IV and V show in detail one form whichthese two embodiments may take.

A suitable source of current is disposed in the handle I l the handleshown in the drawing being illustrative merely. For instance, a batterymay be disposed in this handle I I and as a further example, atransformer may be disposed therein. The light bulb E is threaded into abase I2 so as to be adjustable longitudinally of its axis, and currentis supplied to this lamp E by electrical connection IS. A housing i5 isthreaded on to the base I2, which is in turn mounted on the upper end ofthe handle H, this housing l5 being provided with a chamber foraccommodating the electric lamp E. The wall [6 of this chamber ispreferably rendered dull black in any suitable manner so as not to givereflections.

Instead of directing the light from the lamp E immediately upon thepartially transmissive means, I have retained the handle H and theelectric lamp E in their conventional position, and provide a lateralpassage I I which permits the light from the lamp E to fall upon areflecting mirror 19. This mirror is preferably of the front surfacereflecting type, and is held in place in the light projection passageway20 by a sleeve 2i.

The light reflected by this mirror l9 passes along the projectionpassageway 20 and out through the condensing lens C. I have employed forthis purpose a condensing lens of such focus that the light is directedas slightly divergent rays upon the partially transmissive means R. Inthe instrument shown in Figs. IV and V, this means R is a sheet of clearglass with polished surfaces. This sheet of glass R is held in the lowerrim of a hood 22 by a retaining ring 23.

This hood 22 is fixed on the patients side of a vertically disposedplate 25, with the axis of the hood at such an angle that the sheet ofglass R, which is normal to this axis, receives the light emanating fromthe electric lamp E at the required angle of incidence, hereinapproximately the angle 66 The plate 25 is secured to the housing l byscrews 26, and is provided with a knob 21 for resting against the browof the observer.

A bracket 29 is secured to the base of the plate 25 by screws 30. Thebracket 29 is hollow to provide a guideway for a slide 34, whichaccordingly can be raised and lowered. There is integral therewith, soas to move into and out of alignment with the sight opening 33 in theplate 25 a mount 32. A screw 35 in a slot in the lower portion of theslide 35 secures to the slide a leaf spring 31 so as to press against aball 38 retained within a recess 39 extending through the portion of theslide 34. This ball drops into a slight depression 4D in the bracket 29when the mount 32 is in alignment with the sight opening 33. A crossbar42 disposed in a transverse slot in the slide 34 carries at its endknurled knobs 43 by which the slide 34 may be raised and loweredrelative to the bracket 29. For this purpose slots 44 are provided inthe two sides of the bracket 29.

The polarizing device N which serves as the analyzer is mounted in theupper portion 32 of the slide 34 and retained in its opening by a ring46. It will be apparent from the construction illustrated and describedthat the polarizing device N may be moved into 'or out of alignment withthe sight opening 33, so that the observer may use this analyzer ordispense with its use as he desires.

As previously mentioned, a portion only of the light directed upon thesheet of glass R is reflected to the eye of the patient. The portionwhich passes through the sheet R is of no use, and care should be takento dissipate it as completely as possible. Accordingly, I coat theinterior surface of the hood 22 with a shiny black paint, varnish, orthe like. Whatever light is not absorbed by this shiny black surface isreflected against the opposed face of the plate 25. This opposed face Icover with a dull black covering, such as a coating of black paintwithout gloss. Whatever light is reflected by the inner surface of thehood 22 is to a large extent absorbed by this dull black surface of theplate 25.

Due to the oval cross section of the hood 22, the sheet of glass R isalso oval instead of round, as is suitable for a reflecting surfacearranged at this angle relative to the line of sight.

It will be apparent from the above description that I have provided adiagnostic instrument of this type which is relatively less expensivethan similar instruments employing Nicol prisms 0r similar polarizingdevices for polarizing the light directed upon the surfaces of the eyeto be examined.

It will, furthermore, be apparent that by eliminating such a polarizingdevice between the source of illumination E, and the patients eye, theamount of available illumination for the surfaces to be observed, hasbeen increased.

While I have illustrated and described certain embodiments which myinvention may assume, it

will be understood that the invention may be otherwise embodied andpracticed within the scope of the following claims.

I claim:

1. A diagnostic instrument which may be used in eye examination, saidinstrument having a head with a sight aperture portion for viewing theeye under examination, a transparent reflector supported on said headadjacent said sight aperture portionand with its reflecting surfacelying in a plane so angularly disposed relative to the sight apertureportion as to afford a line of sight through said transparent reflectorand sight aperture, a light source, means on said instrument forsupporting the light source and for directing the light from said sourceto the reflecting surface at substantially the polarizing angle so thatfor the particular transparent medium used for said reflector the lightwill be polarized and will be directed substantially along the line ofsight, transparent reflector and sight aperture portion being supportedso that the reflector will also function as analyzing means thetransparent reflector being positioned at the polarizing angle for thelight reflected back from the eye under examination and passing alongthe line of sight through the transparent reflector and sight aperturewhereby specular reflection from the cornea and lenses in front of thecornea of an eye under observation, returning substantially along saidline of sight, will be reduced and diffused light coming from the insideof said eye will be transmitted to the eye of an individual using saidinstrument when the instrument is supported in its normal operatingposition.

2. A diagnostic instrument which may be used in eye examination, saidinstrument having a head with a sight aperture portion for viewing theeye under examination, a reflective unit comprising a plurality ofcontiguous transparent reflectors supported on said head adjacent saidsight aperture portion and with the reflective surfaces thereof lying inplanes so angularly disposed relative to the sight aperture portion asto afford a line of sight through said transparent reflectors and sightaperture, a light source, means on said instrument for supporting thelight source and for directing the light from said source to thereflecting surfaces at substantially the polarizing angle so that forthe particular transparent medium used for said reflectors the lightwill be polarized and will be directed substantially along the line ofsight, the transparent reflectors and sight aperture portion beingsupported so that the reflectors will also function as analyzing means,the transparent reflectors being positioned at the polarizing angle forthe light reflected back from the eye under examination and passingalong the line of sight through the transparent reflectors and sightaperture whereby specular reflection from the cornea and lenses in frontof the cornea of an eye under observation, returning substantially alongsaid line of sight, will be reduced and diifused light coming from theinside of said eye will be transmitted to the eye of an individual usingsaid instrument when the instrument is supported in its normal operatingposition.

3. A diagnostic instrument which may be used in eye examination, saidinstrument having a head with a sight aperture portion for viewing theeye under examination, a transparent reflector supported on said headadjacent said sight aperture portion and with its reflecting surfacelying in a plane so angularly disposed relative to the sight apertureportion as to afford a line of sight through said transparent reflectorand sight aperture, a light source,

means on said instrument for supporting the light source and fordirecting the light from said source to the reflecting surface atsubstantially the polarizing angle so; that for the particulartransparent medium used for said reflector the light will be polarizedand will be directed substantially along the line of sight, thetransparent reflector and sight'aperture portion being supported so thatthe reflector will also function as analyzing means, the transparentreflector being positioned at the polarizing angle for the,

light reflected back from the eye under examination and passing alongthe line of sight through the transparent reflector and sight aperturewhereby specular reflection from the cornea and lenses in front of thecornea of an eye under observation, returning substantially along saidline of sight, will be reduced and diffused light coming from the insideof said eye will be transmitted to the eye of an individual using saidinstrument when the instrument is supported in its normal operatingposition and a polarizing device mounted on the head on the oppositeside of the sight aperture portion from the transsaid head adjacent saidsight aperture portion 1 and with its reflective surface lying in aplane so angularly disposed relative tothe sight aperture portion so asto afford a line of sight through said transparent reflector and sightaperture, a passageway extending sidewiserelative to said source ofillumination, a passageway angularly disposed relative to said firstpassageway and directed toward the transparent reflector, a lightdeflecting member located adjacent the point of intersection of saidangularly disposed light passageways for receiving light coming fromsaid source of illumination and for directing the light to thereflecting surface of the transparent reflector so that, for theparticular transparent medium used for said reflector, the light will bepolarized and will be directed substantially along the line of sight,the entire assembly being supported so that the reflector will alsofunction as analyzing means whereby specular reflection from the corneaand lenses in front of the cornea of an eye under observation, returningsubstantially along said line of sight, will be reduced and diffusedlight coming from the inside of said eye will be transmitted to the eyeof an individual using said instrument when the instrument is supportedin its normal operating position.

EDGAR D. TILLYER.

